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How does a power supply work?

Power Supply
Power Supplies

The power supply is the heart of any electronic system or machine. In this BLOG article we will explain how a power supply works on a very basic level. You will also learn more about the difference of an AC/DC converter and a DC/DC converter.

How does an AC/DC converter work?

Most of today’s electronic devices and systems require a stable DC voltage. But mains electricity is based on AC voltage. A power supply converts the supplied AC mains on the input to the required DC on the output side. This is why a power supply is also called a converter or transformer.

The DC voltage (e.g. 5 Vdc, 12 Vdc, 24 Vdc, 48 Vdc) is in many cases lower than the original AC voltage, which is typically between AC 100 V and 240 V. The AC voltage depends on the region you are. E.g. the standards in many regions are AC 100-120 V (e.g. USA, Japan) or AC 200-240 V (e.g. Europe, China) and 50 or 60 Hz.

So the main task of an AC/DC converter is to transform the high and dangerous AC to the lower and safe DC required by the device, system or machine. (See graphic 1)

Functionality of industrial AC/DC converters.

Graphic 1: Simplified visualization of the tasks of an AC/DC converter.

Step by step to DC voltage

If we look at the AC diagram (see graph 2) we see a sine wave. This means that the voltage continuously changes its polarity. The frequency of this graph is described in Hertz (Hz). A frequency of 50 Hz means that the voltage changes its polarity 50 times per second.

In the first step, the high AC voltage is converted into a lower AC voltage by a transformer (see graphic 3). The transformer also ensures galvanic isolation and thus safety. The primary circuit (dangerous mains voltage, e.g. 230 V) and the secondary circuit (safe voltage, e.g. 24 V) are separated from each other.

Since most devices require a DC voltage on the input side, the AC voltage must be rectified in the next step. The result of this process is shown in the DC diagram (see graphic 4). After the rectification process, we only see positive polarity. This is realized by a bridge rectifier.

AC voltage from the mains.

Graphic 2: Sine curve of an AC voltage.

Lower AC voltage.

Graphic 3: First, the high AC voltage (100-240V) is converted into a lower one.

Curve of a DC voltage

Graphic 4: Curve of a DC voltage.

Smoothened DC voltage

Graphic 5: Curve of a smoothened DC voltage.

How to get a stable DC at the output?

For a stable DC supply the process of rectification isn’t enough. The heavy peaks in the DC curve need to be smoothened. This is done by the output capacitor in the power supply. The capacitor can store energy very fast, which it supplies between 2 peaks. This process fills the drops to a certain amount and smoothes the curve. The result is a stable DC voltage on the output (see graphic 5), which is supplied to the load. “Load” is the term for the device, system or machine which needs to be supplied with energy.

This is how an AC/DC converter works, explained on a very basic level. But how does it look like if we are facing DC voltage on the input side of the power supply?

Types of power supplies

AC/DC converters

Power supplies for AC/DC conversion, convert an AC voltage to a DC voltage. There are two types of AC/DC power supplies: unregulated and regulated. Regulated power supplies are furthermore categorized into linear and switched-mode power supplies.

DC/DC converters

A DC/DC converter can be used to convert a DC voltage into a higher or lower DC voltage or to refresh DC at the end of long cables.

What is a DC/DC converter?

“DC/DC converter” is a broad generic term. It includes various types of components and devices, from a tiny on-board converter up to a standalone industrial device. The following explanations apply to the latter category, as PULS is specialized in this type of products.

Step-up or step-down DC

There are several tasks where industrial DC/DC converters can be used. One is to convert an existing DC voltage into a lower or higher DC voltage – e.g. stepping up 12 Vdc to 24 Vdc or stepping down 48 Vdc to 24 Vdc.

Refresh DC voltage

DC/DC converters which provide the same voltage on the output side like on the input side are used to refresh the DC voltage. This can be necessary in applications with long cable runs. The voltage drop on power wires is often underestimated.

Remote locations and vehicles

Furthermore DC/DC converters are necessary when the energy source provides a DC voltage, like a battery or a solar panel, for example. Therefore DC/DC converters are often used in remote locations or on trains and other vehicles with its own electrical on-board system.

Regions with unstable mains quality

Many factories work with a DC 200-300 V supply internally – especially in countries where the mains quality is very unstable (e.g. India, Malaysia, etc.). In the semiconductors industry, for example, entire factories are fed via DC. In the event of a power failure, large batteries take over, preventing an entire batch from having to be discarded. Therefore many industrial AC/DC converters can also be operated with a high DC voltage (e.g. DC 110-150 V and even up to DC 300 V) at the input.

Functionality of an industrial DC/DC converter

Graphic 6: Basic functionality of an industrial DC/DC converter.

How does a DC/DC converter work?

An industrial DC/DC converter takes the existing DC voltage at the input. Next, as with the AC/DC converter, a transformer ensures the galvantic isolation and the voltage is stepped up or down to the required output voltage. The galvanic isolation ensures the isolation of the input and output stage of the power supply. This is important for breaking ground loops and ensuring all necessary safety measures.

Afterwards the voltage is smoothened again. On the ouput the device provides a stabilised and galvanically separated DC with a higher, lower or refreshed voltage level.

This BLOG article has explained how power supplies work as a converter on a very general level. However, there are different types of power supplies, which are based on different technologies. E.g. modern switched-mode power supplies are way more complex and offer many additional features that go beyond the actual process of voltage conversion.

We will explain more on this topic in one of our next BLOG articles.